Al-Ma'mun

al-Ma'mun (13 September 786-9 August 833) was the Caliph of the Abbasid Caliphate from 813 to 833, succeeding al-Amin and preceding al-Mu'tasim.

Biography
al-Ma'mun was born on 13 September 786 to Caliph Harun al-Rashid and his Persian wife Marajil, and he served as Governor of Khorasan from 802, while his older brother al-Amin was designated as his father's primary successor. al-Ma'mun was made the secondary successor, who would succeed al-Amin on his death. al-Ma'mun claimed that Harun was ill when he made his decision, so he said that his word was invalid. When Harun died, al-Ma'mun led the army of Khorasan against his brother's Iraqi forces, and from 809 to 827, he fought his brother and rebels in the Fourth Fitna. In 813 he became caliph after capturing Baghdad and executing his brother, and he reigned until 833.

In August 833, al-Ma'mun and those with him sat on a river bank and the water was said to be splendid with a certain kind of dates. He took some dates from an arriving supply convoy and invited those with him to enjoy the dates with the water. All who ate it fell ill, and while some recovered, al-Ma'mun died of illness. He was buried in the Tarsus Grand Mosque in Turkey, and his half-brother al-Mu'tasim succeeded him.